1. Field of the Invention
The present invention relates to an ink jet printing apparatus that performs printing by moving a printing head in directions intersecting with a transfer direction of a printing medium. Particularly, the present invention relates to a recovery method for maintaining absorption capability of an ink absorber. The ink absorber absorbs ink ejected on an area outside the edge portions of the printing medium, when performing so-called “marginless printing” where printing is carried out with no margin provided on the edge portions of the printing medium.
2. Description of the Related Art
In recent years, ink jet printing apparatuses which eject ink from nozzles of a printing head are widely used as computer output apparatuses. Provided are many of such apparatuses which can print an image on the edges of a printing medium and output a printed matter with no margin. In the ink jet printing apparatus that performs “marginless printing,” ink is ejected on an area outside the utmost edges of the printing medium for printing an image. At this time, an ink absorber is provided at a position opposing to a passage where a printing head moves, and absorbs ink in order to prevent ink ejected on such an outside area from polluting the interior of the apparatus.
However, in ink to be used, for example, there is pigmented ink that is not easily absorbed by the ink absorber and such ink tends to be gradually accumulated on the surface of the ink absorber. As the accumulation of ink progresses, various troubles occur such as transfer failure of a printing medium, ink stains on the back surface of the printing medium, damage of an ejection port surface of the printing head due to contact between the ejection port surface and accumulated ink and the like.
Japanese Patent Laid-Open No. 2004-25557 discloses the following technique to solve the foregoing problems. Specifically, by ejecting easily-absorbable ink onto an area of an ink absorber to which hardly-absorbable ink is already applied, the absorption capability of the ink absorber is exerted more and the accumulation of ink on the ink absorber is suppressed.
In the present specification, the ink hardly absorbed by the ink absorber, which easily accumulates on the absorber, is hereinafter called accumulation ink. The ink easily absorbed by the ink absorber, which suppresses the accumulation on the absorber, is hereinafter called suppression ink.
Incidentally, in an ink jet printing apparatus performs “marginless printing,” the amount of ink to be applied per unit area of the ink absorber provided in the apparatus is not uniform.
FIG. 8 is a schematic view for illustrating an ink absorber and positional variations of the amount of ink applied. A printing medium P placed at the position shown in FIG. 8 before starting “marginless printing” is transferred in the transfer direction upon start of printing operation. Then, the printing medium P is positioned so that it's leading portion f (not illustrated) should be disposed above an ink absorber 208A on an area printable by a printing head. After that, the printing head starts printing on a portion in the vicinity of the leading portion f while moving in the main scanning directions in FIG. 8. Here, if the size of the printing medium is assumed to be A4, the ink ejected onto an area outside the printing medium is absorbed by the absorber 208A over the entire area including the right edge portion, the left edge portion and the leading and trailing portion. Additionally, the printing head generally includes a plurality of nozzles in the transfer direction, but, sometimes, not all the nozzles are used at the time of printing the leading portion or the trailing portion in the case of “marginless printing.”
The ink jet printing apparatus intermittently performs a print scan in main scanning directions using the printing head and a transfer operation of the printing medium in the directions intersecting with the main scanning directions, whereby an image is gradually printed. Accordingly, when printing on the leading portion f of the printing medium progresses to an extent that reaches beyond the ink absorber 208A, printing on the leading portion f is completed and no ink is ejected to the leading and trailing portion toward the ink absorber 208A. In other words, the area where the ink is ejected on outside of the printing medium is only the left edge portion and the right edge portion. When this stage is reached, all nozzles of the printing head is used for printing, and therefore the length of the ink absorber 208A in the transfer direction at the right and left edge portions is generally designed to be longer than that of the leading and trailing portion. However, since the size of the printing medium is not limited to A4, the position of the right edge portion varies according to the size of the printing medium taking the left edge portion side as a base. Accordingly, as illustrated in the figure, some positions for the right edge portion where the absorber can be widened according to the type of the printing medium are generally prepared.
When the print scan and the transfer operation are thus carried out and the trailing portion R of the printing medium reaches the vicinity of the absorber 208A, the trailing portion R is printed in a state that a number of nozzles is reduced again. Thereafter, the ink to be ejected on the outside area during the printing on the trailing portion is absorbed over substantially entire absorber 208A including the right edge portion, the left edge portion and the leading and trailing portion, similar to the case of the printing on the leading portion. When the printing on the trailing portion is completed, the printing medium is discharged to the outside of the apparatus.
In the foregoing series of printing operations of one printing medium, it is understood that portions to which the amount of ink is applied most are right and left edge portions in the area of the ink absorber 208A. This is because the ink is continued to be applied to the right end portion and the left edge portion in the series of printing operations, but no ink is applied to the leading and trailing portion during the printing on the central portion of the printing medium. As a result, in the ink jet printing apparatus that performs printing using ink (accumulation ink) which is not easily absorbed by the ink absorber, ink is easily accumulated on the right and left edge portions as compared with the other portions. In other words, in the case of applying suppression ink to suppress the accumulation of ink on the absorber as described in Japanese Patent Laid-Open No. 2004-25557, a necessary amount of suppression ink applied differs depending on the portion of the ink absorber.
However, in the technique described in Japanese Patent Laid-Open No. 2004-25557, suppression ink is ejected from the plurality of nozzles at a fixed drive frequency while moving the carriage having the printing head at a constant speed, so that a substantially constant amount of suppression ink is applied to any portion of the absorber. This causes a problem that the necessary amount of ink applied cannot be obtained according to the amount of accumulation ink applied to the right and left edge portions.